Transparent conductors are used for displays such as liquid crystal displays (LCDs), plasma display panels (PDPs), and electroluminescence panels (organic EL, inorganic EL), and transparent electrodes for solar cells or the like. In addition, transparent conductors are used for electromagnetic insulation films and infrared shield film. For a material of a metal oxide layer of a transparent conductor, ITO, which is a substance obtained by adding tin (Sn) to indium oxide (In2O3), is widely used.
Terminals provided with a touch panel such as smartphones and tablet terminals have been rapidly spreading in recent years. They have a configuration in which a touch sensor part is provided on a liquid crystal panel, and a cover glass is provided on the outermost surface. The touch sensor part is configured with one sheet or two sheets pasted together, each sheet being obtained by forming an ITO film through sputtering on one surface or both surfaces of a glass or a substrate for a film.
In association with upsizing of touch panels and achievement of highly precise touch sensor function, a transparent conductor having a high transmittance and low resistance has been required. It is required for lowering of the resistance of a transparent conductor with an ITO film to thicken the ITO film or to crystalize the ITO film through thermal annealing. However, thickening of the ITO film leads to lowering of the transmittance. In addition, it is typically difficult to perform thermal annealing for a substrate for a film at high temperature. Thus, it is currently difficult to lower the resistance of an ITO film provided on a substrate for a film while the transmittance is kept high.
In such circumstances, a transparent conductive film having a laminate structure of a metal oxide layer containing indium oxide or zinc oxide as a primary component and metal layer has been proposed (e.g., Patent Literatures 1 and 2).